In pulsed light sources or for time-critical applications, it is generally necessary to examine a spectrum simultaneously in various spectral regions. Polychromators including concave gratings in a Paschen-Runge mounting are customarily employed for this purpose. These polychromators have adjustable slits in which masks are arranged and the light intensity at the location of the slit is measured by means of photodetectors. The photodetectors measure the respective total intensity. The information about spectral resolution in the vicinity of the spectral line at the slit is lost.
In complicated spectra, the selected spectral lines may be interfered with considerably by lines from the same or another element being examined by the light source, and additionally, continuous radiation may contribute an amount to the total radiation which cannot be neglected. In these cases, knowledge of the spectral resolution in the vicinity of the spectral line is absolutely necessary since only in that way can the net line intensity of the selected line be determined.
A single spectral region can be measured simultaneously by means of one row of photodiodes having a high spectral and time resolution and accuracy. However, a respective additional row of photodiodes is needed for each other spectral region.
A row of photodiodes includes up to 2048 photodiodes which are arranged at spacings of 25 .mu.m. These photodiodes simultaneously measure the light intensity present at their locations. In this way, a measurement is taken of the spectral intensity distribution of a spectral region.